Agreed, and I don't think it's an attitude thing either, a lot of them are just not physically capable of playing this way. A squad overhaul will be needed whether the club likes it or not, or Amorim will likely fail.
It's a grand total of maybe 3 current starters at a push that can't run back. Amad, Garnacho, Bruno, Ugarte, Mazraoui, the CBs (who usually play almost all their football in one half of the pitch), Dalot, Mount, Højlund, Kobbie, Antony, even big uncle Casemiro all have shown great inclination to run back and recover the ball.
Dalot has shown he has a great motor on him but may sometimes lose concentration and Casemiro when being tasked to cover the pitch has sometimes been slow to react, but under Ruud in a more compact system, he got around the pitch fine in attack and defence.
Kobbie runs out of gas early but that will naturally improve as he develops physically.
Where's the squad overhaul needed for non physically capable players?
I think bad habits have just crept in for some of the players.
Eriksen obviously can't but is not a regular starter, neither is Shaw (another who can't) right now but I suspect his future may be at CB.
Rashford looks like he won't, but I don't know if he can't, Zirkzee is another one that looks dodgy physically but going by his stats in Italy, it may just be a catching up to the speed of the league issue.
I wouldn't call selling these four an overhaul, considering only Rashford is currently considered a recent automatic starter.